Elastomeric polymers, both homopolymers and polymers of more than one monomer, are well known in the art and include natural rubbers as well as a wide variety of synthetic materials. A particularly useful class of synthetic elastomers is the class of thermoplastic elastomers which demonstrates elastomeric properties at ambient temperatures but which is processable at somewhat elevated temperatures by methods more conventionally employed for non-elastomeric thermoplastics. Such thermoplastic elastomers are illustrated by a number of types of block polymers including, for example, block polymers of alkenyl aromatic compounds and conjugated alkadiene. Block polymers of styrene and butadiene are illustrative. This particular type of block polymer is well known in the art and a number are commercial, being marketed by Shell Chemical Company as KRATON.RTM. Thermoplastic Rubber.
The properties of block polymers, even containing the same or similar monomers, will vary considerably with the arrangement of the monomeric blocks within the block polymer and with the relative molecular weight of each block. To obtain good elastomeric properties a so-called "hard" phase, e.g., a polymerized alkenyl aromatic compound portion, of the molecule must be at least a terminal or outer portion of the polymeric molecule with the "rubber" phase, e.g., a polymerized alkadiene portion of the molecule being internal. If a block polymer contains the rubber phase as the outer portion of the molecule and the hard phase as an internal portion, the polymer will not demonstrate the desired elastomeric properties and will be somewhat waxy in character with little tensile strength.
It is also known that certain of the properties such as resistance to oxidation of this class of block polymers are improved by the selective hydrogenation of some or all of the carbon-carbon unsaturation in the polyalkadiene or aliphatic portion of the molecule and, on occasion, by the hydrogenation of substantially all the carbon-carbon unsaturation including that unsaturation in the poly(alkenyl aromatic compound) or aromatic portion of the molecule. A number of the selectively hydrogenated block polymers are also well known and commercial, being marketed by Shell Chemical Company as KRATON G.RTM. Thermoplastic Rubber.
An alternate method of modifying selected properties of the block polymers is to provide polarity or functionality within the block polymer as by introducing functional groups as substituents within the molecule or by providing one or more additional blocks within the polymeric structure which are polar in character.
An example of the former method of introducing carboxylic acid functionality is the introduction of functional substituents onto the aromatic rings of a block copolymer in which the carbon-carbon unsaturation of the aliphatic portion has been selectively hydrogenated. This type of functionalization is accomplished by the successive steps of metallation, carboxylation and acidification. This overall carboxylation process is considered conventional. Illustrative of the latter method comprising the introduction of blocks containing functional groups are the polymers of McGrath et al, published European Patent Application 298,667, which includes at least one block of polymerized alkyl methacrylate. The three block polymers of McGrath et al, as produced, are polyalkadiene-polystyrene-poly(alkyl methacrylate) materials and thus are not true thermoplastic elastomers by virtue of the hard or polystyrene phase being an internal portion of the molecule and the rubber or polyalkadiene phase being terminal. It would be of advantage to provide block polymers, functionalized by the presence of additional blocks containing functional groups, which exhibit properties of thermoplastic elastomers.